Recently, an opportunity to handle a color image as digital data has increased by the spread of image-related equipments such as digital cameras and color printers, and the improvement of the computer's performance. However, an image quality of a color image taken by a digital camera or the like does not always satisfy the user. For example, an illumination light might badly affect the color balance. In such a case, an originally white object is faintly colored by other colors. Therefore, in order to obtain an image that satisfies the user, a technique to correct the color balance (especially, white balance) is desired. However, it is difficult to correct the color balance in a case where there are a lot of pixels with chromatic colors in the image, or the like.
For example, JP-A-2000-165906 (Patent Document 1) discloses a technique to correct the white balance by avoiding the influence of portions having the chromatic colors in the image. That is, the luminance information and the chroma information are extracted from color image data read from an image memory, a region recognized as a white and recognized as preset colors near white in all pixels of the color image data is determined, and the coefficient for the image processing is calculated based on the mean value of each color component in the region and is outputted. Then, an image processor receives the coefficient for the image processing and a processing flag as inputs, and automatically carries out a white balance correction processing for the image data read from the image memory based on these inputs.
However, according to the aforementioned technique, there is a possibility that the correction from a light color to a white color is wrongly judged and such a wrong correction is carried out, when there is originally no white portion, but there is, for example, a light color portion in the original image. It will be explained specifically by using image examples of FIGS. 8A and 8B. FIGS. 8A and 8B show image examples in a case where, for example, a plant was photographed by a digital camera or the like.
The example of FIG. 8A includes a brown region 10, a light purple region 11, and a green region 12. On the other hand, the example of FIG. 8B includes a brown region 20, a white region 21, and a green region 22. That is, flower colors are different between FIGS. 8A and 8B, and there is no white portion in the example of FIG. 8A. In such a case, when correcting the image of FIG. 8A by using the aforementioned background art, the light purple region 11 is normally identified as an correction target and is corrected to the white color. Thus, it is corrected to the image as shown in FIG. 8B. When the light purple region 11 was an originally white flower region and became light purple by receiving the influence of, for example, an illumination light, a proper correction was carried out. Meanwhile, when the light purple region 11 was an originally light purple flower region and the correction was essentially unnecessary, an improper correction was carried out. Therefore, in such a case, it is not appropriate to automatically carry out the correction according to the judgment that it is a light color near white.
Thus, according to the aforementioned background art, there was a possibility that the wrong correction is carried out for the image having no white region originally.